Solar Shed

Chronicles of my efforts to install a solar powered air conditioner into our shed.

Current Goal: 4 hours runtime

Current Ability: 10 minutes runtime

Current configuration:

(4) 100W Mono panels

(1) 20A Solar Charge Controller – MPPT (2 Panels)

(1) 20A Solar Charge Controller – PWM (2 Panels)

(1) 20A Solar Charge Controller – PWM (unused)

(1) 40A Triple CB

(1) 250A Termination Block

(1) 1500W Inverter – Pure Sine

(1) 150A ANL Fuse

(2) 12V Deep Cycle Marine Battery

(1) 410W Window AC unit

Test Conditions:

Batteries fully charged

11AM – Fall

4 panels providing approx 275w

Test Result:

1100AM – SYSTEM OFF – 14V – 0 watts

1100AM – SYSTEM START – 13.8V – 60 watts load

1102AM – COMPRESSOR START – 12.9V -350 watts load (with 1300w short peak)

1110AM – 12.2V – 390 watts load


1112AM – 12.8V – 0 watts load

Next steps:

With the current configuration, I feel I can safely run the Air Conditioner for 15 minutes without damaging the batteries. That is obviously unacceptable.

Going to add (2) more 100W mono panels to try and balance the amount of power going out with what is coming in…

Future Plans:

(2) Lithium Iron Phosphate 100Ah batteries – If I had these now I could get several hours of runtime in the dark, and probably hit my target of 4hrs/day no sweat, but they are super pricey so I’m exploring every alternative first

I would hate not to get full use of the batteries I have, which should be a few more years, thinking of adding old car battery to the mix if I need more power, but need to read up about marine and car batteries in parallel and if that would do more harm than good.

(1) 150F super-capacitor – This should keep the compressor from drawing so hard on the batteries, which I’ve seen peak to 1300w on startup, on battery alone to the Air Conditioning has tripped the inverter protection mechanism, I think supercapacitor would prevent that, and be a really good buffer because when things start up, the solar is not always charging the batteries because sometimes they are fully charged, it seems to take a few minutes before the charge controllers start dumping out power, but I need it from the start with these batteries, and this seems like a great solution!

(1) 150A Low Voltage disconnect – Had some close calls leaving things on, SLA batteries should not be drained to less than 50%, this device could save my batteries by disconnecting the load automatic when it gets too low

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